Mercury Levels in Illinois Rain and Snowfall Are Declining

[March 31, 2008]  CHAMPAIGN -- Every state except for Alaska and Wyoming has issued an advisory warning pregnant women and children to limit fish consumption, due to highly toxic methyl mercury that builds up in fish tissue. Information from the Mercury Deposition Network, which monitors mercury concentration and deposition in rain and snowfall, indicates that mercury levels in the atmosphere are falling, but not by much.

Precipitation deposits mercury from the atmosphere to Illinois waters, although mercury occurs naturally in Illinois soils, according to David Gay, acting coordinator of the National Atmospheric Deposition Program, which coordinates the Mercury Deposition Network at the Illinois State Water Survey in Champaign.

Illinois rainfall averages 10 nanograms of mercury per liter of precipitation, which is about average compared with other states. Peak concentrations occur in summer. Nationwide, the highest deposition of mercury from the atmosphere occurs along the Gulf of Mexico and in Florida.

Mercury is converted to methyl mercury in water and sediments, and it accumulates from small organisms up the food chain to large predator fish species.

When humans consume mercury, it takes about 70 days for half the mercury that was ingested to be removed. It is particularly dangerous for unborn and young children. Large doses of methyl mercury could cause damage to the heart, kidneys and central nervous system.

Mercury is emitted to the atmosphere and surface water from many natural sources, including volcanoes and wildfires. Man-made sources include coal combustion, medical waste incineration and chlorine production, among others.

Mercury concentrations found in Illinois waters and in fish may not have originated from Illinois industry.

"It's not necessarily a local problem," said Gay. "Mercury stays in the environment for six months to two years. You can't say that the mercury came from a particular smokestack. It could just as easily have come out of China."

Mercury concentrations in precipitation are measured weekly at 100 sites throughout the U.S., including six sites in Canada, and reported to the Mercury Deposition Network.

Measurement data are available at http://nadp.sws.uiuc.edu/mdn/.

[Text from file received from Illinois State Water Survey]